Japanese scientists have been successful in moving an object in a three-dimensional space through a complex system of acoustic levitation, surpassing previous research endeavors that lifted the objects in two dimensions.

In order to move expanded polystyrene particles of 0.6 mm and 2
mm in diameter, the Japanese scientists at the University of
Tokyo and the Nagoya Institute of Technology had to place the
objects inside a complex set-up of four arrays of speakers.

Using a refinement of the existing technology of sound wave
management, bubbles, a screw and a tiny piece of wood were
airlifted and moved around in all direction within the
experiment’s confines.

“We considered extended acoustic manipulation whereby
millimeter-sized particles were levitated and moved
three-dimensionally by localized ultrasonic standing waves, which
were generated by ultrasonic phased arrays,” the study
stated.

The experiment machine is comprised of audio speakers capable
generating inaudible high frequencies sound waves that intersect
inside a restrained space. The waves then generate a
“moveable ultrasonic focal point,” frequency noise
greater than 20kHz, where crossover creates standing waves. Some
waves are kept in constant position, serving as a suspending
force, while other waves are used to support a floating object
jammed in the standing waves.

“Our manipulation system has two original features. One is
the direction of the ultrasound beam, which is arbitrary because
the force acting toward its center is also utilized. The other is
the manipulation principle by which a localized standing wave is
generated at an arbitrary position and moved three-dimensionally
by opposed and ultrasonic phased arrays,” the study said.

The practice of moving tiny objects acoustically along the fixed
axes is not new, but it was previously applied to 2D, starting
from 1975.

“The essence of levitation technology is the countervailing
of gravity. It is known that an ultrasound standing wave is
capable of suspending small particles at its sound pressure
nodes,” Yoichi Ochiai from University of Tokyo said.

Currently, acoustic levitators are used mostly in industry and
for researchers of anti-gravity effects such as at NASA.